<br><font size=2 face="sans-serif">For what it's worth,</font>
<br>
<br><font size=2 face="sans-serif">What do you consider large and what
kind of method for downscaling you wish to use?</font>
<br>
<br><font size=2 face="sans-serif"> I do this in GRASS using the
r.neighbors command, </font><a href=http://grass.fbk.eu/grass64/manuals/html64_user/r.neighbors.html><font size=2 face="sans-serif">http://grass.fbk.eu/grass64/manuals/html64_user/r.neighbors.html.
I've done an averaging method to convert a 20 ft elevation grid
( statewide coverage) of approximately 7 billion cells to an
averaged 60 ft grid ( 777 million cells) by performing a 3x3 neighbor
hood analysis on the 20 ft grid, setting the GRASS workspace resolution
to 60 ft and multiplying the 20ft grid created by the 3x3 neighborhood
analysis by 1 to create a new grid (</font><a href=http://grass.fbk.eu/grass64/manuals/html64_user/r.mapcalculator.html><font size=2 face="sans-serif">http://grass.fbk.eu/grass64/manuals/html64_user/r.mapcalculator.html)
. GRASS will take the value of the center averaged 20 ft cell
in the 60ft block as the value of the cell in the new 60 ft raster.
</font></a></a>
<br>
<br><font size=3>options for r.neigbors calculations are : average,median,mode,minimum,maximum,range,stddev,sum,variance,diversity,interspersion
</font>
<br>
<br>
<br><font size=3>Doug</font>
<br>
<br>
<br><font size=2 face="sans-serif">Doug Newcomb
<br>
USFWS<br>
Raleigh, NC<br>
919-856-4520 ext. 14 doug_newcomb@fws.gov<br>
---------------------------------------------------------------------------------------------------------<br>
The opinions I express are my own and are not representative of the official
policy of the U.S.Fish and Wildlife Service or Dept. of the Interior.
Life is too short for undocumented, proprietary data formats.</font>
<br>
<br>
<br>
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<tr valign=top>
<td width=40%><font size=1 face="sans-serif"><b>Tim Keitt <tkeitt@gmail.com></b>
</font>
<br><font size=1 face="sans-serif">Sent by: gdal-dev-bounces@lists.osgeo.org</font>
<p><font size=1 face="sans-serif">12/15/2011 01:17 PM</font>
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<td>
<div align=right><font size=1 face="sans-serif">To</font></div>
<td><font size=1 face="sans-serif">"Andreas H." <lists@hilboll.de></font>
<tr valign=top>
<td>
<div align=right><font size=1 face="sans-serif">cc</font></div>
<td><font size=1 face="sans-serif">gdal-dev@lists.osgeo.org</font>
<tr valign=top>
<td>
<div align=right><font size=1 face="sans-serif">Subject</font></div>
<td><font size=1 face="sans-serif">Re: [gdal-dev] re-gridding to a coarser
grid</font></table>
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<table>
<tr valign=top>
<td>
<td></table>
<br></table>
<br>
<br>
<br><tt><font size=2>If you need complete control, and your data are not
too massive in<br>
number, I have had good results pushing pixel coordinates as points<br>
into postgis and then using spatial queries to aggregate in various<br>
ways (eg averages a hexagonal grid). It seems round-about, but it<br>
works. I've actually done it on some pretty massive grids.<br>
<br>
THK<br>
<br>
On Wed, Dec 14, 2011 at 7:26 AM, Andreas H. <lists@hilboll.de> wrote:<br>
> Travis,<br>
><br>
> thanks for your answer!<br>
><br>
> Regarding the resampling methods: Do they all just interpolate the
data? I<br>
> mean, when downsampling, usually I would use mean() or something similar<br>
> to fill the new (coarser) grid cells. Doas gdalwarp actually do this
and<br>
> I'm not able to understand the documentation, or is it different?<br>
><br>
> Thanks again!<br>
> Andreas.<br>
><br>
><br>
>> Andreas,<br>
>><br>
>> gdalwarp can be used to resample images using the -tr flag or
-ts flag.<br>
>><br>
>> For example resample 1m image to 10m using cubic resampling and<br>
>> "target resolution'<br>
>><br>
>> gdalwarp -r cubic -tr 10 10 input_1m.tif output_10m.tif<br>
>><br>
>> You may have an issue determining the output resolution as I believe<br>
>> the resolution will be in decimal degrees rather than arc-seconds.<br>
>><br>
>> Regards<br>
>><br>
>> On 13 December 2011 14:52, Andreas H. <lists@hilboll.de>
wrote:<br>
>>> Hi,<br>
>>><br>
>>> let's say I have a GeoTIFF file with a global grid in a 30
arc-second<br>
>>> resolution. Which would be the appropriate GDAL command to
spatially<br>
>>> down-sample this file to say 0.125°?<br>
>>><br>
>>> Thanks for your insight,<br>
>>> Andreas.<br>
>>> _______________________________________________<br>
>>> gdal-dev mailing list<br>
>>> gdal-dev@lists.osgeo.org<br>
>>> </font></tt><a href="http://lists.osgeo.org/mailman/listinfo/gdal-dev"><tt><font size=2>http://lists.osgeo.org/mailman/listinfo/gdal-dev<br>
>><br>
><br>
><br>
> _______________________________________________<br>
> gdal-dev mailing list<br>
> gdal-dev@lists.osgeo.org<br>
> </font></tt><a href="http://lists.osgeo.org/mailman/listinfo/gdal-dev"><tt><font size=2>http://lists.osgeo.org/mailman/listinfo/gdal-dev<br>
<br>
<br>
<br>
-- <br>
Timothy H. Keitt<br>
</font></tt><a href=http://www.keittlab.org/><tt><font size=2>http://www.keittlab.org/<br>
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